MONDAY, February 13, 2012 (Health.com) — Older people who consume a diet very high in calories may be increasing their risk of mild cognitive impairment (MCI), the memory loss and mental-function problems that sometimes precede Alzheimer's disease.

In a new study of more than 1,200 people in their 70s and 80s, Mayo Clinic researchers found that men and women who consumed at least 2,143 calories per day had more than double the odds of having MCI compared with those who consumed 1,526 calories per day or less.

Preliminary findings from the study are slated to be presented at the annual meeting of the American Academy of Neurology in April. Unlike research published in medical journals, the study has not yet been thoroughly vetted by other experts in the field.

The study does not prove that high-calorie diets directly cause MCI, nor does it indicate a link between overeating and dementia. Some people with MCI do go on to develop Alzheimer's disease and other forms of dementia, but that does not happen in every case.

Lead researcher Yonas Geda, MD, an associate professor of neurology and psychiatry at the Mayo Clinic in Scottsdale, Ariz., stresses that the results will need to be confirmed in future studies. At this point, he says, any interpretations or conclusions are "speculation."

For instance, Geda says, the findings should not be construed as a recommendation for calorie intake. He and his colleagues divided the study participants into equal thirds according to their average intake (thus the oddly specific cutoff points)—an essentially "arbitrary" method that is commonly used in research but has little bearing on calorie targets for individuals, he says.

Federal health officials recommend that women over age 50 consume between 1,600 and 2,200 calories per day, depending on how physically active they are, and that men in the same age group aim for between 2,000 and 2,800 calories. But the guidelines emphasize the importance of balancing calorie intake and physical activity in order to maintain a healthy weight, not specific calorie amounts.

This emphasis on calorie balance points to a key limitation of the new study: Although Geda and his colleagues took into account extenuating factors such as body mass index, genetic susceptibility to Alzheimer's disease, and medical history (including heart disease, strokes, and diabetes), they had no data on exercise and physical activity. Future studies will need to examine both sides of the calorie equation, Geda says.

The study participants, all of whom hailed from Olmsted County, Minn., filled out a detailed questionnaire about their typical diet over the previous year. They also underwent a series of memory and cognitive tests. None had dementia, but the researchers determined from the test results that 163 had MCI.

MCI is "the gray zone between normal aging and dementia," Geda says. "People with MCI are not demented [but] they are forgetful a little more than expected for their age." This forgetfulness goes beyond senior moments (such as misplacing car keys), and might include forgetting airplane flights and other important appointments, he adds.

Although it remains to be proven, there is a plausible scientific explanation for how overeating might erode mental function. Consuming a high-calorie diet may spur production of harmful, oxygen-containing molecules, and these so-called oxidative radicals may accumulate in cells and cause neurons to break down, Geda says.